Menu

Corrosion control in a steam boiler


Company: Citro misr, Cairo Egypt
  Description of the problem and its negative consequences
In the chemical industry, big amounts of steam are needed to heat up different processes. The client uses several steam boilers, with a total capacity of more than 100m3 per hour. The feed water is treated chemically. The de-mineralized (DM) water gets aggressive and together with the high temperatures inside the boiler, corrosion begins at all surfaces in contact with the water. The client added inhibitors to prevent corrosion, which is the normal procedure if running a steam boiler. The reality has shown, that even by using corrosion inhibitors, there is corrosion anyhow. This corrosion leads, on-hand to iron or rust in the steam, which might cause additional corrosion in the following pipe system. This corrosion may lead to a stock removal on the surfaces, which is responsible for a shorter lifetime of the boilers. This can be easy checked by the blowdown the water of the boiler.
In a steam boiler having corrosion problems, the blowdown water is not clear but has a brown color, caused by the iron or Rust Fe2O3.

The solution
There was one Pursanova TM installed at the feeding pipe of the boiler. Due to safety reasons, there was first no change in the adding of inhibitors against corrosion.
  In which way the customer checked the results of the trial
The iron content in the steam and the blowdown pipe was regularly checked. (The steam is essential for the production, without steam they have to stop working.) Therefore, no changes to the existing setup of adding chemicals were made. During the following weeks, the iron in the steam has gotten less and less, and finally stabilized at a very low level. The corrosion was less than before when observed from the outside.
To avoid any risk, the addition of the inhibitors was stopped not before six weeks ahead of the regular production break where service is made on the boiler. This was done, to be able to assure visually the function of Pursanova TM, by checking the appearance of the inner surfaces of the boiler. It was seen, that most of the surface was now black, coated with saturated iron, only a few red spots have remained.
After seeing this result the client has decided to stop adding corrosion inhibitors. To ensure the results and for safety reasons, the steam is regularly checked for iron. Today the client saves not only the chemicals but as well the costs for service of the dosing systems.
No final data is available concerning the lifetime of the boiler. It is assumed that the lifetime has increased due to almost no iron being found any more in the steam.
A lot of customers are reusing the condensate from the steam consumers. This condensate is coming back and refused to produced new steam. Pursanova TM is able to solve these problems in the condensate as well. See this topic in a case study on corrosion in a condensate system.